Proton conductors in liquid form

ABSTRACT

The invention is a proton conductor in liquid form, comprising a mixture of the following components: (a) an acid addition salt of a nitrogen base, having the formula: ##STR1## wherein: Z 1 , Z 2 , Z 3  and Z 4 , identical or different, each represent a group --N═ or --C(Y i )═ in which Y i  represents a hydrogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, a fluoroalkyl radical having 1 to 20 carbon atoms, or an oxoalkyl or azaalkyl radical having 1 to 20 carbon atoms, with the proviso that at least one and at most two of the groups Z 1 , Z 2 , Z 3  and Z 4  represents --N═, two adjacent carbon atoms being optionally hydrogenated and the nitrogen base optionally being part of a polymeric network, and X -   represents an anion derived from an acid selected from the group consisting of sulfonic acids of formula R F  SO 3  H, sulfonimides of formula (R F  SO 2 ) (R&#39; F  SO 2 )NH and methylides of formula (R F  SO 2 ) (R&#39; F  SO 2 ) CH 2  or (R F  S 2 ) (R&#39; F  SO 2 ) (R&#34; F  SO 2 )CH, in which R F , R&#39; F  and R&#34; F  each represents a radical F(CF 2 ) n  --, n being comprised between 0 and 6, the acid optionally being part of a polymeric network; and (b) a nitrogen base having the formula: ##STR2##  in which Z 1 , Z 2 , Z 3  and Z 4  have the aforesaid meanings, the nitrogen base optionally being part of a polymeric network; components (a) and (b) being present in proportions to form a composition having a melting point lower than 25° C. The proton conductor is useful as an electrolyte in various electrochemical systems.

FIELD OF THE INVENTION

The present invention relates to novel proton conductors in liquid formand to their use as liquid, gel or polymer electrolytes in variouselectrochemical systems.

BACKGROUND OF THE INVENTION

The most common proton conductors are obtained by doping water with anacid such as HCl or H₂ SO₄, or a base such as KOH or NH₃. Thus, aqueoussolutions of sulfuric acid have a high proton conductivity greater than10⁻² S·cm⁻¹ and solutions of potassium hydroxide which are also veryconducting are widely used as electrolytes in Nickel-Cadmium.

Proton conductors requiring the presence of water in order to functiongenerally have a field of use limited in temperature due to theevaporation of the water and a field of redox stability limited to thatof water. The presence of water also usually induces corrosion phenomenawithin the systems utilizing these electrolytes.

In order to overcome these redhibitory problems with respect to certainapplications, a number of works have born on the study of anhydrousproton conductors. From the various classes of materials resulting fromthese researches, there have been more particularly obtained anhydrousproton conductors by substituting the aqueous solvent withnon-hydroxylic solvating polymers such as polyethylene oxide,polyvinylpyrrolidone, polyethyleneimine or polyaminopropylsiloxane.

By doping these polymers with acids or bases, one obtains anhydrousproton conductors. For examples, dissolving orthophosphoric acid H₃ PO₄in polyethylene oxide (POE) enables one to obtain an acidic protonconductor, and dissolving sulfonamide H₂ NSO₂ NH₂ in the same polymerenables one to obtain a basic proton conductor.

These electrolytes are useful for making electrochemical systems,particularly light-modulating systems, but they still have majordrawbacks. Proton conductors obtained by dissolving H₃ PO₄ in POE arecorrosive due to the high acidity of the medium (pK_(a) ≈0). On thecontrary, the high basicity (pK_(a) ≈11-12) of proton conductorsobtained by dissolving sulfonamides in POE limits their uses. Indeed, inthe presence of many electrode materials containing metallic species,there is formed a passivation layer which is a poor conductor ofmetallic cations complexed with sulfamide. On the other hand, theseelectrolytes are poor conductors at low temperature.

SUMMARY OF THE INVENTION

In order to overcome the above drawbacks, the inventors have found quitesurprisingly that binary mixtures of certain nitrogen bases belonging tothe azole family with appropriate acid addition salt of these nitrogenbases form proton conductors having a melting point lower than roomtemperature, a weak vapor tension and a conductivity similar to thatobtained in aqueous medium.

According to the present invention, there is thus provided a protonconductor in liquid form, comprising a mixture of the followingcomponents (a) and (b):

a) an acid additive salt of a nitrogen base, having the formula:##STR3## wherein: Z₁, Z₂, Z₃ et Z₄, identical or different, eachrepresent a group --N═ or --C(Y_(i))═ in which Y_(i) represents ahydrogen atom, a linear or branched alkyl group having 1 to 20 carbonatoms, a fluoroalkyl radical having 1 to 20 carbon atoms, or an oxoalkylor azaalkyl radical having 1 to 20 carbon atoms, with the proviso thatat least one and at most two of the groups Z₁, Z₂, Z₃ et Z₄ represents--N═, two adjacent carbon atoms being optionally hydrogenated and thenitrogen base optionally being part of a polymeric network, and

X⁻ represents an anion derived from an acid selected from the groupconsisting of sulfonic acids of formula R_(F) SO₃ H, sulfonamides offormula (R_(F) SO₂) (R'_(F) SO₂)NH and methylides of formula (R_(F) SO₂)(R'_(F) SO₂)CH₂ or (R_(F) SO₂) (R'_(F) SO₂) (R"_(F) SO₂) CH, in whichR_(F), R"_(F) and R"_(F) each represents a radical F(CF₂)_(n) --, nbeing comprised between 0 and 6, the acid optionally being part of apolymeric network; and

b) a nitrogen base having the formula: ##STR4## in which Z₁, Z₂, Z₃ andZ₄ have the aforesaid meanings, the nitrogen base optionally being partof a polymeric network;

components (a) and (b) being present in proportions to form acomposition having a melting point lower than 25° C.

The invention also relates to a liquid electrolyte consisting of aproton conductor as defined above.

The invention is also directed to a polymer electrolyte comprising aproton conductor as defined above, dissolved in a polymer comprising atleast on polar group.

Preferably, the composition comprising the mixture of components (a) and(b) is substantially eutectic.

Examples of nitrogen bases include the azoles of formula: ##STR5##wherein Y_(i) has the aforesaid meaning.

Use can also be made of partially hydrogenated azoles such as theimidazolines of formula: ##STR6## wherein Y_(i) has the aforesaidmeaning.

The selection of the nitrogen base enables one to control the pH of theproton conductors according to the invention. Thus, the binary mixturestriazole/triazolium have a pK_(a) of the order of 2, the binary mixturesimidazole/imidazolium have a pK_(a) of the order of 7 and the binarymixtures imidazoline/imidazolinium have a pK_(a) of the order of 10.

Examples of acids include triflic acid, bisfluorosulfonimide,bistrifluoromethanesulfonimide, bistrifluoromethanesulfonylmethane,tristrifluoromethane-sulfonylmethane and trisfluorosulfonylmethane.

The binary mixtures comprising the above components (a) and (b) areanhydrous proton conductors. Indeed, a nitrogen base which is protonatedis capable of transferring its proton to a non-protonated nitrogen baseaccording to a Grotthus mechanism, permitting the displacement of theproton in these media. For example, in the case of the binary mixtureimidazole/imidazolium triflate having an eutectic composition (3:1molar), the conductivity of this mixture is greater than 10⁻³ Ω⁻¹ ·cm⁻¹at 25° C. Such a mixture thus constitutes a neutral anhydrous protonconductor having a high conductivity.

The proton conductors according to the invention are particularlyinteresting for light-modulating systems called electrochrome.Electrochrome systems generally utilize films of wide band gapsemi-conducting materials such as H.sub. WO₃ or IrO₂ H_(x), H_(x) TiO₂,H_(x) Ta₂ O₅, H_(x) MnO₂, H_(x) CO₂, H_(x) NiO₂, x being typicallycomprised between 0 and 0.4, in which the concomitant injection ofextraction of protons and electrons results in a variation of theoptical absorption or reflectance in the visible or infrared spectrum.

Other electrochrome systems utilize soluble precursors of highly coloredfree radicals such as viologens ("Weitz blue"), the coloration of whichis obtained by reduction, or 1,4-tetraalkyl aryl-diamines ("Wursterblue"), the coloration of which is obtained by oxidation. However, thesecompounds when in the colored state have only a limited stability,particularly with respect to light and oxygen, and cannot be utilized inwindowpanes or display systems which are exposed to natural light.

The proton conductors according to the invention rely on a new principalof reversible formation of colored species, by electrochemical reactionsinvolving the injection of two electrons and one or two protons, asfollows:

[ox]⁺ +2e⁻ +H⁺ →[red]

[ox]⁻ +2e⁻ +2H⁺ →[red]⁻

[ox]+2e⁻ +2H⁺ →[red]

wherein passing from ox to red corresponds to a change of color. In thiscase, the colored species are not radicals and have a stability which ismarkedly improved over radical systems. The proton conductors accordingto the invention not only have a high protonation power and a pHcontrolled by the selection of the azole-type heteroatom, but also amuch wider operating temperature range and a solubilizing power towardsorganic molecules, with respect to aqueous media.

The present invention therefore also provides an electrochrome systemcomprising two transparent semi-conducting electrodes arranged inspaced-apart opposed relationship to one another, each electrode beingfixed on one side thereof to a transparent support and comprising on another side thereof a coating of a wide band gap semi-conductingmaterial, and a polymer electrolyte as defined above, disposed betweenthe electrodes and contacting the coatings of semi-conducting material.

The invention is also directed to an electrochrome system comprising twotransparent semi-conducting electrodes arranged in spaced-apart opposedrelationship to one another, each electrode being fixed on one sidethereof to a transparent support, and a polymer electrode as definedabove, disposed between the electrodes and contacting the other side ofeach electrode, the polymer electrolyte comprising at least one redoxcoloring agent added thereto.

According to the invention, there is also provided an electrochromesystem comprising two transparent semi-conducting electrodes arranged inspaced-apart opposed relationship to one another, each electrode beingfixed on one side thereof to a transparent support and one of theelectrodes comprising on the other side thereof a coating of a wide bandgap semi-conducting material, and a polymer electrolyte as defined abovedisposed between the electrodes and contacting the coating ofsemi-conducting material. The polymer electrolyte comprises at least oneredox couple added thereto, the redox couple being complementary to thewide band gap semi-conducting material.

Non-limiting examples of molecules capable of undergoing reversiblecolor changes include the following:

    __________________________________________________________________________    reduced form            oxidized form                                         __________________________________________________________________________     ##STR7##                                                                                              ##STR8##                                              ##STR9##                                                                                              ##STR10##                                             ##STR11##                                                                                             ##STR12##                                             ##STR13##                                                                                             ##STR14##                                             ##STR15##                                                                                             ##STR16##                                             ##STR17##                                                                                             ##STR18##                                            __________________________________________________________________________

In the above formulas, R₁ to R₁₀ are alkyl, aryl, arylalkyl or alkylarylgroups optionally containing oxa, aza, thia substituents or halogens,nitro, cyano, carboxylate, sulfonate, onium groups, in the alkyl chainsor in the rings.

R₁₁ to R₁₆ are aryl, alkylaryl, heterocycle groups optionally containingoxa, aza, thia substituents or halogens, nitro, cyano, carboxylate,sulfonate, onium groups, in the alkyl chains or in the rings.

Examples of coloring agents or redox couples providing a color change bythe application of current include:

leuco(violet crystal) ←→ crystal violet (violet oxidized form),

leuco(malachite green) ←→ malachite green (green oxidized form),

leuco(methylene blue) ←→ methylene blue (blue oxidized form),

bis(4-hydroxyphenylamine) ←→ imidazolium salt of indophenol (redoxidized form),

3,4-dihydroxy-9,10-anthraquinone (alizarine, red reduced form) ←→3,4,9,10-tetrahydroxy-anthracene,

4,4'bis(4-nitrophenylformazan)-3, 3'-methoxy-biphenyl (blue reducedform) ←→ tetranitrotetrazolium blue cation,

triphenyl formazan (blue reduced form) ←→ 2,3,5 triphenyl-2H-tetrazoliumcation,

1,4-diaminophenyl-hydrazino-1-naphthalene ←→1,4-diaminophenyl-azo-1-naphthalene (Fat brown RR, chestnut oxidizedform).

The redox couples can be associated in a complementary manner, that is,one of the reagents undergoes a color change by reduction whereas itscomplement undergoes a color change by oxidation. It is thus possible toincorporate into the medium molecules undergoing redox reactions withouta color change, thereby enabling the reaction of formation of thecoloring agent to be effected at a single electrode. For example,compounds involving the formation and cleavage of disulfide bonds suchas dimercaptothiadiazole, mercaptomethyltetrazole, the correspondinganions of which are stables in the electrolyte of the invention, can becited.

It is also possible to associate with the above families of coloringagents organometallic molecules exhibiting stable redox couples such asferrocene or its derivatives, or to use counter-electrodes on which awide band gap semi-conducting material such as H_(x) WO₃, IrO₂ H_(x),H_(x) TiO₂, H_(x) Ta₂ O₅, H_(x) MnO₂, H_(x) NiO₂, H_(x) CoO₂ (x beingtypically comprises between 0 and 0,4), is deposited.

The proton conductors according to the invention are also interestingfor electrochemical generators, electrochemical supercapacitorscomprising at least one carbon electrode, at least one metallic oxideelectrode or at least one polymer having redox properties. The protonconductors according to the invention can be used as anhydrous proticsolvents having a high solvating power and also has solvents foreffecting chemical, photochemical or electrochemical reactions.

In addition to all the advantages mentioned above, the proton conductorsaccording to the present invention form polymer electrolytes when theyare mixed with polymers containing polar groups, such as polyethers,polyesters, polyethyleneimine, polyacrylonitrile, vinylidenepolyfluoride, or polyvinyl butyrale. Membranes having both a goodmechanical properties and a high conductivity are thus obtained.Moreover, the conductivity of the liquid, gel or polymer protonconductors according to the present invention can be increased by addingat least one polar solvent which is hardly volatile, suchdimethylformamide, dimethylacetamide, tetraalkyl-sulfamides or glymes.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become moreclearly apparent from the following description of preferredembodiments, with reference to the accompanying drawings, in which:

FIG. 1 is a partial schematic sectional view of an electrochrome systemcomprising a polymer electrolyte according to the invention;

FIG. 2 is a partial schematic sectional view of another electrochromesystem comprising a polymer electrolyte according to the invention;

FIG. 3 represents the phase diagram of the binary mixtureimidazole/imidazolium triflate;

FIG. 4 represents the phase diagram of the binary mixtureimidazole/imidazolium bis (trifluoromethane-sulfonimide);

FIG. 5 represents the phase diagrams of the binary mixtureimidazole/imidazolium triflate, in the presence and absence ofpolyethylene oxide or polyethylene glycol;

FIG. 6 is a diagram showing the variation of the conductivity of thebinary mixture imidazole/imidazolium triflate as a function of thetemperature, compared to other electrolytes;

FIG. 7 represents the discharge curve obtained with an electrochemicalgenerator comprising a binary mixture triazole/triazoliumbisfluoro-sulfonimide; and

FIG. 8 represents the cycling curve obtained with an electrochromesystem comprising a polymer electrolyte formed of the binary mixture1,2,3-triazole/1,2,3-triazolium bis (trifluoromethanesulfonimide)dissolved in polyethylene oxide.

DESCRIPTION OF PREFERRED EMBODIMENTS

The electrochrome system illustrated in FIG. 1 comprises two transparentsemi-conducting electrodes 10 arranged in spaced-apart opposedrelationship to one another, each electrode 10 being fixed on one sidethereof to a transparent support 12 such as glass and comprising on theother side thereof a coating 14 of a wide band gap semi-conductingmaterial. A polymer electrolyte 16' according to the invention isdisposed between the electrodes 10 and contacts the coatings 14 ofsemi-conducting material. The electrochrome system illustrated in FIG. 2is similar to the one shown in FIG. 1, with the exception that theelectrodes 10 are not provided with a coating 14, the polymerelectrolyte 16' comprising instead two complementary redox coloringagents added thereto. The application of a voltage to electrodes 10results in a color change of the coatings 14 in the case of theelectrochrome system shown in FIG. 1 and a color change of the redoxcoloring agents present in the polymer proton electrolyte 16' in thecase of the electrochrome system shown in FIG. 2.

FIG. 3 represents the diagram of the binary mixtureimidazole/imidazolium triflate. As shown, this binary mixture has aneutectic plateau for a molar ratio imidazole/salt (I/S) equal to 3, witha melting point of about 12° C. FIG. 4, on the other hand, representsthe phase diagram of the binary mixture imidazole/imidazoliumbistrifluoromethanesulfonimide. As shown in FIG. 4, this binary mixturehas an eutectic plateau for a molar ratio I/S equal to 4, with a meltingpoint of about -10° C. Generally, the binary mixtureimidazole/imidazolium bisfluorosulfonimide at its eutectic composition(molar ratio I/S equal to 4) has a melting point lower than -20° C. Thenature of the substituents has also an influence on the properties ofthe liquid conductors; thus, in the case of the binary mixture2-hexylimidazole/2-hexylimidazolium triflate, the temperature of theeutectic plateau for a molar ratio I/S equal to 3 or 4 is lower than-10° C.

FIG. 5 shows that the addition of 20 wt. % of polyethylene oxide to abinary mixture imidazole/imidazolium triflate having a molar ratio I/Sequal to 4 hardly modifies the phase diagram of the system, the systembeing now in the form a film of polymer electrolyte which isparticularly suitable for fabricating thin film electrochemical systems:light-modulating systems such as described above, generators,supercapacitors, sensors, etc. FIG. 6 provides the conductivity of thispolymer proton electrolyte and enables one to compare its conductivitywhich those of other polymer electrolytes which are proton conductors:an electrolyte obtained by mixing orthophosphoric acid and polyethyleneoxide (PEO/H₃ PO₄), an electrolyte obtained by mixing orthophosphoricacid and polyethylene imine (PHI/H₃ PO₄), an electrolyte obtained bymixing sulfamide and polyethylene oxide (PEO/sulfamide). Therefore, theconductivity of the liquid or polymer electrolytes obtained from thebinary mixtures according to the invention can be increased by adding apolar solvent which is hardly volatile, such as dimethylformamide orglymes.

The following non-limiting examples illustrate the invention.

EXAMPLE 1

To a solution in 15 ml of ether of 1.36 g (20 mmoles) of imidazole wereadded 5.62 g (20 mmoles), of bistrifluoromethanesulfonimide (CF₃ SO₂)₂NH (sold by Fluka), the mixture was maintained under agitation for 1hour and a precipitate was thereafter recovered by filtration on frittedglass having a No. 3 porosity. After drying, the imidazolium salt ofbistrifluoromethanesulfonimide of formula: ##STR19## was quantitablyrecovered.

Crushing in a glove box of a molar mixture of four moles of imidazolesfor pool of imidazolium salt enabled one to obtain a liquid conductorhaving a melting point lower than room temperature. This liquidconductor has a high proton conductivity of about 10⁻³ S·cm⁻¹ at 20° C.

EXAMPLE 2

In a globe box under argon, a solution in 50 ml of methyl formiate of6.81 g (100 mmoles) of imidazole, 5.62 g (20 mmoles) ofbistrifluoromethanesulfonimide (CF₃ SO₂)₂ NH (sold by Fluka) and 2.49 gof polyethylene oxide having a mass M_(W) =5×10₆ (20 wt. % based on thesalt) was prepared. This solution was then spreaded on a polypropylenefilm. After 24 hours in the glove box, a film of transparent polymerelectrolyte having good mechanical properties was obtained.

EXAMPLE 3

In a glove box under argon, a thin film electrochemical generator ofpolymer technology was made utilizing as electrolyte the binary mixtureimidazole/imidazolium bistrifluoromethanesulfonimide at its eutecticcomposition (4:1 molar), by superposing the following layers:

an anode constituted by a mixture of anatase titanium dioxide TiO₂ (45vol. %), Shawinigan black (5 vol. %), the above liquid electrolyte (40vol. %) and polyethylene oxide having a mass M_(W) =3×10⁵ (10 vol. %)deposited on a current collector of stainless steel;

a cathode constituted by a mixture similar to that of the anode, butsubstituting for TiO₂ manganese dioxide MnO₂, previously reduced with anequivalent of hydrazine and deposited on a current collector ofstainless steel; and

an electrolyte film constituted by a mixture of the above liquidelectrolyte (80 wt. %) and polyethylene oxide (20 wt. %).

After assembly the whole was sealed in a button shaped batterieshousing. This electrochemical generator initially in a discharge statewas cycled between 1.2 V and 500 mV at a charging/discharging rate ofC/10. A hundred cycles were thus obtained while maintaining 90% of thecapacity at the first discharge. This generator had a useful energydensity of about 100 Wh/kg, the energy density calculated by taking intoaccount only electroactive materials being 160 Ah/kg or 709 Ah/l.

An electrochemical generator was also made utilizing the binary mixtureimidazoline/imidazolinium bistrifluoromethanesulfonimide at its eutecticcomposition and gave similar performances.

EXAMPLE 4

In a Warner & Pfilder extruder under argon atmosphere and operating inan anhydrous chamber, polyethylene oxide having a mass M_(W) =3×10⁵ inthe form of pellets with a diameter of 2 mm was introduced at oneextremity and a mixture of imidazole, 2-hexylimidazoliumbistrifluoromethanesulfonimide, hydrogenated iron fluoride H_(x) FeF₃crushed in grains having a size less than 5 μm, Shawinigan black,KETJENBLACK® K600 (trademark, sold by AKZO) and silica particles (soldunder the trademark AEROSIL R974 by Degussa) where introduced into theextruder. The components were introduced in proportions such that H_(x)FeF₃ represents 45% of the total volume, Shawinigan black 3%,KETJENBLACK® K600 1%, the silica particles 1%, the polyethylene oxide 5%and the other components representing 45% of the total volume; the molarratio imidazole/2-hexylimidazolium bistrifluoromethane sulfonimide being4 to 1. The whole was extruded at a temperature of 100° C. in the formof a band having a width of 14 cm and a thickness of 120 μm, thiscathode film being deposited directly onto a sheet of stainless steelhaving a thickness of 8 μm.

During the process, the composite cathode film was itself covered with afilm of electrolyte having a thickness of 30 μm and obtained byextrusion of a mixture of polyethylene oxide with a mass M_(W) =9×10₅(17 wt. %), silica particles (AEROSIL R974) and a mixture of imidazoleand 2-hexylimidazolium bistrifluoromethanesulfonimide (80 wt. %, molarratio 4:1).

During the process, the electrolyte film deposited on the cathode wasitself covered with an anode film obtained under the same conditions asthe cathode film, but substituting anatase TiO₂ for H_(x) FeF₃. Thewhole was then laminated with a sheet of stainless steel having athickness of 8 μm.

This electrochemical generator initially in a discharge state was cycledbetween 1.2 V and 500 mV at a charging/discharging rate of C/10. Onethousand cycles were thus obtained while maintaining 78% of the capacityat the first discharge.

EXAMPLE 5

An electrochemical generator similar to that described in Example 3 wasmade, but utilizing on the one hand organic electroactive materials,either an anthrahydroquinone (oxanthranol)-based anode and atetrachlorohydrotuinone (chloranil)- based cathode and, on the otherhand, a binary mixture triazole/bisfluorosulfononimide, at its eutecticcomposition and gelled with polyvinylidene fluoride (sold by Montedison)instead of polyethylene oxide.

The discharge curve obtained at a discharging rate of C/30 is shown inFIG. 7. In this figure, the voltage of generator, U, expressed in mV isgiven in ordinate, and the rate of use of the electroactive materials,x, expressed in % is given in abscissa.

This generator has an energy density of 120 Ah/kg calculated by takinginto account only the electroactive materials.

EXAMPLE 6

An electrochemical supercapacitor was made utilizing ruthenium dioxideRuO₂ -based electrode. This type of supercapacitor takes advantage ofthe phenomenon of pseudo-insertion of the proton in these oxides. Theelectrodes were obtained by vacuum deposition. The supercapacitor wasassembled utilizing two of these electrodes and an electrolyteconstituted of the binary mixture 1,3,4-triazole/1,3,4-triazoliumtrisfluoro-sulfonylmethylide at its eutectic composition.

This supercapacitor was cycled between 0 and 1 V at acharging/discharging rate of 10 C. More than 300000 cycles were effectedunder these conditions, the capacity at the 300000th cycle still beingequal to 70% of the capacity of the first cycle. This supercapacitor hasan energy density greater than 5 Wh/kg and can furnish a power greaterthan 1 kW/kg.

EXAMPLE 7

An electrochemical supercapacitor was made utilizing activatedcarbon-based electrodes. These electrodes were composites obtained fromcarbon fiber and aluminum fiber in a reducing medium. The electrodeshaving a thickness of 150 μm were placed on either side of a microporouspolyethylene having a thickness of 40 μm, the whole was impregnated withthe binary mixture pyrazole/pyrazolium bis(trifluoromethanesulfonyl)methide at its eutectic composition, then sealed in a button-shapedbattery housing, in a glove box. Good performances were obtained withthis super-capacitor, and more than 200000 cycles ofcharging/discharging between 0 and 1 with an energy density greater than10 Wh/l and a delivered power greater than 1500 W/l were effected.

EXAMPLE 8

An electrochrome system was made in a glove box under argon, utilizingas electrolyte the binary mixture 1,2,3-triazole/1,2,3-triazoliumbistrifluoromethanesulfonimide at its eutectic composition (molar ratio4:1), by superposing the following layers:

a transparent electrode obtained by depositing on a glass plate a layerof hydrogenated iridium oxide H_(x) IrO₂ and a conducting underlayer oftin oxide;

a film of transparent polymer electrolyte constituted of a mixture ofthe above liquid electrolyte (80 wt. %) and polyethylene oxide (20 wt.%); and

a transparent electrode constituted of a layer of tungsten trioxide WO₃and a conducting underlayer of tin oxide.

This electrochrome enabled one to obtain a variation of the opticalabsorption from 80% in the discolored state to 30% in the colored state.

The cycling curve obtained with the above electrode at acharging/discharging rate of 10 C. is shown in FIG. 8. In this figure,the coulombic capacitance relative to that of the first cycle, C,expressed in percentage is given in ordinate, and the number of cycles,n, expressed in thousands of cycles is given in abscissa.

EXAMPLE 9

An electrochrome was made by dissolving two complementary coloringagents in the binary mixture imidazole/imidazoliumbistrifluoromethanesulfonimide at its eutectic composition. In a glovebox, 1.75 g (5 mmoles) of imidazolium bistrifluoromethanesulfonimide and1.36 g (20 mmoles) of imidazole were crushed together. Afterwards, tothe binary mixture were added 16.5 mg (50 μmoles) of leuco(malachitegreen), in the reduced state which is colorless, and 30.8 mg (50 μmoles)of 3-(4,5-dimethylthiazolyl-2-yl)-2,5-diphenyl-2H-tetrazolium (MTT)bistrifluoromethanesulfonimide, in the oxidized state which is colorless(obtained by anionic exchange in water from the bromide). 8 wt. % ofsilica particles (AEROSIL R 974) were then added. The viscous liquidobtained was deposited between two glass plates covered with aconductive layer of tin indium oxide (ITO). After having sealed theassembly to render it airtight, a voltage of 1300 mV was applied to theexterior with a potentiostat. The system then became colored, theoxidized form of the leuco(green malachite) and the reduced form of theMTT each exhibiting an intense absorption band in the visible spectrum.By applying a voltage of -500 mV, a relatively rapid discoloration ofthe system (less than 60 s) was observed. Such an electrochrome systemhas a long life and is easy to use, even in the case of systems having alarge size (greater than m²) which utilize glass as well as a suitablytreated polymer as transparent conducting electrode. Moreover, theenergy necessary for maintaining the coloration is relatively low, lessthan 1 W/m².

EXAMPLE 10

An electrochrome system similar to that described in Example 9 was made,but utilizing as coloring agents N,N,N',N'-tetramethylphenylenediamine(colorless reduced state) and dimethylviologenbistrifluoromethanesulfonimide (colorless oxidized state). Thiselectrochrome system also becomes colored when applying a voltage to thetwo electrodes. Surprisingly, this system exhibits an importantstability despite the radical mechanism involved during the coloration.The liquid electrolyte, in addition to solubilizing the coloring agents,enables the radicals to be stabilized.

EXAMPLE 11

An electrochemical supercapacitor was made utilizing the binary mixturetriazole/triazolebistrifluoromethanesulfonimide and ruthenium oxideRuO2.

EXAMPLE 12

An electrochemical supercapacitor was made utilizing the binary mixtureimidazolium/imidazolium-tris (fluorosulfonyl)methide and activatedcarbon oxide electrodes, and adding a glyme as plastifying agent.

EXAMPLE 13

An electrochrome system H_(x) IrO2/WO3 was made utilizing the binarymixture triazole/triazolium triflate to which was added polyethyleneoxide diacrylate and a sensitizing agent (Irgacure) and crosslinking thewhole under U.V. radiation.

EXAMPLE 14

An electrochrome with dyes was made utilizing two complementary dyesdissolved in a salt of tristrifluoromethanesulfonylmethide.

We claim:
 1. A proton conductor in liquid form, comprising a mixture ofthe following components (a) and (b):a) an acid addition salt of anitrogen base, having the formula: ##STR20## wherein: Z₁, Z₂, Z₃ and Z₄,identical or different, each represent a group --N═ or --C(Y_(i))═ inwhich Y_(i) represents a hydrogen atom, a linear or branched alkyl grouphaving 1 to 20 carbon atoms, a fluoroalkyl radical having 1 to 20 carbonatoms, or an oxoalkyl or azaalkyl radical having 1 to 20 carbon atoms,with the proviso that at least one and at most two of the groups Z₁, Z₂,Z₃ and Z₄ represents --N═, two adjacent carbon atoms being optionallyhydrogenated and the nitrogen base optionally being part of a polymericnetwork, andX⁻ represents an anion derived from an acid selected fromthe group consisting of sulfonic acids of formula R_(F) SO₃ H,sulfonimides of formula (R_(F) SO₂) (R'_(F) SO₂)NH and methylides offormula (R_(F) SO₂) (R'_(F) SO₂)CH₂ or (R_(F) SO₂) (R'_(F) SO₂) (R"_(F)SO₂) in which R_(F), R'_(F) and R"_(F) each represents a radicalF(CF₂)_(n) --, n being comprised between 0 and 6, the acid optionallybeing part of a polymeric network; and b) a nitrogen base having theformula: ##STR21## in which Z₁, Z₂, Z₃ and Z₄ have the aforesaidmeanings, the nitrogen base optionally being part of a polymericnetwork; andwherein components (a) and (b) are present in proportions toform a composition having a melting point lower than 25° C.
 2. A protonconductor according to claim 1, wherein the composition comprising themixture of components (a) and (b) is substantially eutectic.
 3. A protonconductor according to claim 1, wherein component (a) is an acidaddition salt of a nitrogen base consisting of an imidazole having theformula: ##STR22## wherein Y_(i) represents a hydrogen atom, a linear orbranched alkyl group having 1 to 20 carbon atoms, a fluoroalkyl radicalhaving 1 to 20 carbon atoms, or an oxoalkyl or azaalkyl radical having 1to 20 carbon atoms.
 4. A proton conductor according to in claim 1,wherein component (a) is an acid addition salt of a nitrogen baseconsisting of a 1,2,3-triazole having the formula: ##STR23## whereinY_(i) represents a hydrogen atom, a linear or branched alkyl grouphaving 1 to 20 carbon atoms, a fluoroalkyl radical having 1 to 20 carbonatoms, or an oxoalkyl or azaalkyl radical having 1 to 20 carbon atoms.5. A proton conductor according to claim 1, wherein component (a) is anacid addition salt of a nitrogen base consisting of a 1,3,4-triazolehaving the formula: ##STR24## wherein Y_(i) represents a hydrogen atom,a linear or branched alkyl group having 1 to 20 carbon atoms, afluoroalkyl radical having 1 to 20 carbon atoms, or an oxoalkyl orazaalkyl radical having 1 to 20 carbon atoms.
 6. A proton conductoraccording to claim 1, wherein component (a) is an acid addition salt ofa base consisting of a pyrazole having the formula: ##STR25## whereinY_(i) represents a hydrogen atom, a linear or branched alkyl grouphaving 1 to 20 carbon atoms, a fluoroalkyl radical having 1 to 20 carbonatoms, or an oxoalkyl or azaalkyl radical having 1 to 20 carbon atoms.7. A proton conductor according to claim 1, wherein component (a) is anacid addition salt of a nitrogen base consisting of an imidazolinehaving the formula: ##STR26## wherein Y_(i) represents a hydrogen atom,a linear or branched alkyl group having 1 to 20 carbon atoms, afluoroalkyl radical having 1 to 20 carbon atoms, or an oxoalkyl orazaalkyl radical having 1 to 20 carbon atoms.
 8. A proton conductoraccording to claim 1, wherein the acid is selected from the groupconsisting of triflic acid, bisfluorosulfonimide,bistrifluoromethanesulfonimide, bistrifluoromethanesulfonylmethane,tristrifluoromethane-sulfonylmethane and trisfluorosulfonylmethane.
 9. Aproton conductor according to claim 3, wherein component (a) is anaddition salt of imidazole with triflic acid.
 10. A proton conductoraccording to claim 3, wherein component (a) is an addition salt ofimidazole with bisfluorosulfonimide.
 11. A proton conductor according toclaim 3, wherein component (a) is an addition salt of imidazole withbistrifluoromethanesulfonimide.
 12. A proton conductor according toclaim 3, wherein component (a) is an addition salt of 2-hexylimidazolewith triflic acid.
 13. A proton conductor according to claim 1, whereincomponent (b) is a nitrogen base consisting of an imidazole having theformula: ##STR27## wherein Y_(i) represents a hydrogen atom, a linear orbranched alkyl group having 1 to 20 carbon atoms, a fluoroalkyl radicalhaving 1 to 20 carbon atoms, or an oxoalkyl or azaalkyl radical having 1to 20 carbon atoms.
 14. A proton conductor according to claim 1, whereincomponent (b) is a nitrogen base consisting of a 1,2,3-triazole havingthe formula: ##STR28## wherein Y_(i) represents a hydrogen atom, alinear or branched alkyl group having 1 to 20 carbon atoms, afluoroalkyl radical having 1 to 20 carbon atoms, or an oxoalkyl orazaalkyl radical having 1 to 20 carbon atoms.
 15. A proton conductoraccording to claim 1, wherein component (b) is a nitrogen baseconsisting of a 1,3,4-triazole having the formula: ##STR29## whereinY_(i) represents a hydrogen atom, a linear or branched alkyl grouphaving 1 to 20 carbon atoms, a fluoroalkyl radical having 1 to 20 carbonatoms, or an oxoalkyl or azaalkyl radical having 1 to 20 carbon atoms.16. A proton conductor according to claim 1, wherein component (b) is anitrogen base consisting of a pyrazole having the formula: ##STR30##wherein Y_(i) represents a hydrogen atom, a linear or branched alkylgroup having 1 to 20 carbon atoms, a fluoroalkyl radical having 1 to 20carbon atoms, or an oxoalkyl or azaalkyl radical having 1 to 20 carbonatoms.
 17. A proton conductor according to claim 1, wherein component(b) is a nitrogen base consisting of an imidazoline having the formula:##STR31## wherein Y_(i) has the aforesaid meaning.
 18. A protonconductor according to claim 1, wherein component (b) is a nitrogen baseconsisting of imidazole.
 19. A proton conductor according to claim 1,wherein component (b) is a nitrogen base consisting of 2-hexylimidazole.20. A proton conductor according to claim 1, comprising a mixture of 3moles of imidazole and one mole of imidazolium triflate.
 21. A protonconductor according to claim 1, comprising a mixture of 4 moles ofimidazole and one mole of imidazolium bis(trifluoromethanesulfonimide).22. A proton conductor according to claim 1, comprising a mixture of 4moles of imidazole and one mole of imidazolium bisfluorosulfonimide. 23.A proton conductor according to claim 1, comprising a mixture of 3 or 4moles of 2-hexylimidazole and one mole of 2-hexylimidazolium.
 24. Aliquid electrolyte consisting of a proton conductor as defined inclaim
 1. 25. A polymer electrolyte comprising a proton conductor asdefined in claim 1, dissolved in a polymer comprising at least one polargroup.
 26. A polymer electrolyte according to claim 25, wherein thepolymer is polyethylene oxide.
 27. An electrochrome system comprisingtwo transparent semi-conducting electrodes arranged in spaced-apartopposed relationship to one another, each of said electrodes being fixedon one side thereof to a transparent support and comprising on an otherside thereof a coating of a wide band gap semi-conducting material, anda polymer electrolyte as defined in claim 25, disposed between saidelectrodes and contacting the coatings of semi-conducting material. 28.An electrochrome system comprising two transparent semi-conductingelectrodes arranged in spaced-apart opposed relationship to one another,each of said electrodes being fixed on one side thereof to a transparentsupport, and a polymer electrode as defined in claim 25, disposedbetween said electrodes and contacting the other side of each electrode,said polymer electrolyte comprising at least one redox coloring agentadded thereto.
 29. An electrochrome system comprising two transparentsemi-conducting electrodes arranged in spaced-apart opposed relationshipto one another, each of said electrodes being fixed on one side thereofto a transparent support and one of said electrodes comprising on another side thereof a coating of a wide band gap semi-conductingmaterial, and a polymer electrolyte as defined in claim 25, disposedbetween said electrodes and contacting the coating of semi-conductingmaterial, said polymer electrolyte comprising at least one redox coupleadded thereto, said redox couple being complementary to said wide bandgap semi-conducting material.
 30. An electrochrome generator comprisingan anode, a cathode and an electrolyte as defined in anyone of claim 24,disposed between said anode and s aid cathode.
 31. An electrochemicalsupercapacitor comprising an anode, a cathode and an electrolyte asdefined in claim 24, disposed between said anode and said cathode.
 32. Asensor comprising a proton conductor as defined in claim
 1. 33. Ananhydrous protic solvent consisting of a proton conductor as defined inclaim
 1. 34. Use of an anhydrous protic solvent as defined in claim 33,for carrying out chemical, photochemical or electrochemical reactions.